how to drive high side mosfet

[seyyah]

high side mosfet driver circuit

Can you suggest a way that allows a mosfet which is at the high side to be drived from the logic level. Please offer a way which can be done using seperate or basic components (transistors, resistors etc) not ICs.
I'll also be pleased to hear IC offers but i need to accomplish it using seperate parts for now.

 

[flatulent]

mosfet high side driver

you can use from the high rail a resistor connected to the high side FET gate. Then the collector of an NPN transistor whose emitter is to ground. Drive the base from your logic through a series resistor. When the NPN is off, the resistor from the positive supply to the MOS gate makes Vgs=0 and the MOS is off. When the NPN is conducting, the MOS Vgs=Vcc and the MOS is conducting. If there is a breakdown problem on the MOS Vgs, put a Zener or resistor between the gate and the NPN so that when the NPN is on, the Vgs is acceptable.

 

[seyyah]

high side mosfet drive

You mean this? If so this won't work.

 

[flatulent]

bootstrap circuit mosfet

You will need a PMOS on the high side. Otherwise the top NMOS will only pull the output to within Vth of the supply. This can easily be 4 V in some NMOS devices.

 

[mrcube_ns]

high side mosfet

It's simple. Just add PMOS to drive gate on high NMOS (something like darlington but with two different type of transistors).

Everything else is same.


Mr.Cube

 

[Mr.Cool]

high side fet

that was exactly the answer i was thinking of when u asked for high side driver. but then i saw your circuit. i think you will run into a couple of problems when trying to use that king of circuit normally reserved for power switch application and not high side drive of a half bridge. half bridges are usually used because of high power and high speed switching (>20kHz). that transistor may not like the fact that a high DC bus is in use. and the resistor in the schematic is likely very large value, probably 100Meg which means your drive current (used to charge the gate capacitance of switch) is severly limited. now your mosfet turn on time is slow and may cause shoot through or over heat the device cause of long time in linear mode.

i would consider using a bootstrap circuit. cheap and easy.

Mr.Cool

 

[seyyah]

mosfet bootstrap circuit

Yeah i've heard about the bootstrap. I think that will solve my problem. Do you know how to realize that? What's the logic behind it and how will be the circuit? Any source about this will welcome.

 

[Mr.Cool]

mosfet high side

you can find all you need by google your answer. application notes at web sites such as international rectifier or fairchildsemi. i could be wrong, but i think microchip dot com also has some app notes on this subject. there is nothing i can give u that can't be found by simple net search.

good luck!
Mr.Cool

 

[seyyah]

high side mosfet circuit

Actually i did the web search. But i couldn't obtain clear documents. But with combining different documents and a bit thinking, i think i understood the subject.

 

[Mr.Cool]

fet high side driver

ah you see.. this is one of the greatest characteristics of an engineer. they have no idea how to do, but they go out and do it anyways.

some things to keep in mind about bootstraping is that it is a "cheap and dirty" solution. but lets assume your requirements for project are not that strict, so this is acceptable. bootstraps work best in an environment where the duty cycle does not reach 100% very often. therefore, good for DC/DC converters, but not good for motor drives. this is because the capacitor charge is used to keep the high side fet ON. but what if the fet needs to be on for a very long time (100% duty cycle) and low switching frequency? now you need a lot of charge in the cap, and are given no time in which to replenish.. of course even this problem can be solved given some thought..

Mr.Cool

 

[seyyah]

high side mosfet driver

Yes you are right. I wonder are there any other ways, which is "clean", to replace bootstrap.

 

[wky]

high side drive

See this appnote

 

[rauol]

driver high side pmos

you can use driver from CLARE, it has photodiodes connected in series which will generate voltage which will be enough to turn on a mosfet.
switching speeds are low.

 

[SPATAN]

You can used opto TLP250 .
It's designed for mosfet drive and isolate input and output.

 

[probert]

driving high-side mosfet

Hi,

I'm using this circuit for a Half-Bridge application. Snubber circuits are currently missing from it, so I have some voltage swings to eliminate.

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Regards,
probert

 

[BOHDA]

mosfet high side drive

On internet are a huge number of data and AN.I just put here Motorola old file[Now for application notes you have to visit ONsemiconductors]

 

[rauol]

how to drive the high side mosfets

If your dutycycle is <50% u can use a transformer

if dutycycle is upto 100% u can use a floating power and optoisolator combination.